1. Field of Use
This disclosure is generally directed an apparatus for assisting transfer of a developed image to a copy substrate in an electrostatographic printing machine. The apparatus enhances physical contact between the copy substrate and the developed image, wherein the apparatus includes a conductive blade member for eliminating image defects.
2. Background
Generally, the process of electrostatographic copying is initiated by exposing a light image of an original document onto a substantially uniformly charged photoreceptive member. Exposing the light image onto the charged photoreceptive member discharges a photoconductive surface thereof in areas corresponding to non-image areas in the original document while maintaining the charge in image areas, thereby creating an electrostatic latent image of the original document on the photoreceptive member. Thereafter, developing material comprising charged toner particles is deposited onto the photoreceptive member such that the toner particles are attracted to the charged image areas on the photoconductive surface to develop the electrostatic latent image into a visible image. This developed image is then transferred from the photoreceptive member, either directly or after an intermediate transfer step, to an image support substrate such as a copy sheet, creating an image thereon corresponding to the original document. The transferred image is typically affixed to the image support substrate to form a permanent image thereon through a process called “fusing”. In a final step, the photoconductive surface of the photoreceptive member is cleaned to remove any residual toner particles thereon in preparation for successive imaging cycles.
The electrostatographic copying process described above is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrostatographic printing applications such as, for example, digital printing where the latent image is produced by a modulated laser beam, or ionographic printing and reproduction, where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
The process of transferring charged toner particles from an image bearing member, such as the photoreceptive member, to an image support substrate, such as the copy sheet is accomplished at a transfer station, wherein the transfer process is enabled by electrostatically overcoming adhesive forces holding the toner particles to the image bearing member. In a conventional electrostatographic machine, transfer is achieved by transporting the image support substrate into the area of the transfer station where electrostatic force fields sufficient to overcome the forces holding the toner particles to the photoconductive surface are applied to attract and transfer the toner particles over onto the image support substrate. In general, such electrostatic force fields are generated via electrostatic induction using a corona generating device, wherein the copy sheet is placed in direct contact with the developed toner image on the photoconductive surface while the reverse side of the copy sheet is exposed to a corona discharge. This corona discharge generates ions having a polarity opposite that of the toner particles, thereby electrostatically attracting and transferring the toner particles from the photoreceptive member to the image support substrate. An exemplary corotron ion emission transfer system is disclosed in U.S. Pat. No. 2,836,725.
During electrostatic transfer of a toner image to a copy sheet, it is generally necessary, or at least desirable, for the copy sheet to be in uniform intimate contact with the photoconductive surface and the toner powder image developed thereon. Unfortunately, however, the interface between the photoreceptive surface and the copy substrate is not always optimal. In particular, non-flat or uneven image support substrates, such as copy sheets that have been mishandled, left exposed to the environment or previously passed through a fixing operation (e.g., heat and/or pressure fusing) tend to promulgate imperfect contact with the photoreceptive surface of the photoconductor. Further, in the event the copy sheet is wrinkled, the sheet will not be in intimate contact with the photoconductive surface and spaces or air gaps will materialize between the developed image on the photoconductive surface and the copy sheet where there is a tendency for toner not to transfer across these gaps, causing variable transfer efficiency and, in extreme cases, creating areas of low or no transfer, resulting in a phenomenon known as image transfer deletion. Clearly, an image transfer deletion is very undesirable in that useful information and indicia are not reproduced on the copy sheet.
As described, the typical process of transferring development materials in an electrostatographic system involves the physical detachment and transfer-over of charged toner particles from an image bearing photoreceptive surface into attachment with an image support substrate via electrostatic force fields. Thus, a very critical aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the adhesive forces acting on the toner particles as they rest on the photoreceptive member. Another critical aspect of the transfer process is focused on the application of mechanical force on the copy sheet in the transfer region for overcoming the adhesive forces acting on the toner particles as they rest on the photoreceptive member.
It would be desirable to provide a transfer assist device that meets the mechanical and electrical needs for transferring toner particles from the photoreceptive member to the copy sheet.